1. Field of the Invention
The present invention relates to an improved oxygen recycle type ozonizing apparatus.
2. Description of the Prior Arts
Ozone is used as an oxidizing agent in a water treatment or a production process because its strong oxidizing function and sterilizing function. It has been known that more than two times the amount of ozone is obtained by using oxygen gas as a raw material instead of air in an ozonizer thereby reducing a substantive power comsumption of the ozonizer. However, in such case, an oxygen recycle system is required for using the oxygen gas as a raw material effectively.
FIG. 1 is a diagram of an embodiment of the conventional water treating apparatus using ozone which has an oxygen recycle system.
In FIG. 1, the reference numeral (1) designates an ozonizer, (2) designates a reaction tower, (3) designates a blower, (4) designates a cooling and moisture-removing device, (5) designates an air-diffusing plate, (6) designates a container for oxygen gas and (10) designates an adsorption type gas drier.
The operation of the conventional apparatus will be described.
Oxygen gas as the raw material is fed from the container (6) and is supplied to the ozonizer (1) in which an ozonized oxygen having an ozone concentration of several percents is produced and the resulting ozonized oxygen is consumed by the discharging in water as fine bubbles from the orifices of the air-diffusing plate (5) at the bottom of the reaction tower (2). During the bubbling, most of the oxygen rises to water surface to exit from the top of the reaction tower (2) whereas a small portion of oxygen is dissolved in the water and is discharged with the water. The discharged water is sucked and compressed by the blower (3) and is cooled at about 5.degree. C. by the cooling and moisture-removing device (4) to which a cooled brine is fed from a refrigerator (not shown) to condense water component contained in the gas and the resulting water is removed as a drainage. The gas from the cooling and moisture-removing device (4) is fed to the adsorption type gas drier (10) wherein the gas is dried to give the dew point of lower than -40.degree. C. and then is recycled to the container (6) as the oxygen gas source. The recycle system of this type is referred to as an oxygen recycle system. An amount of oxygen equal to a sum of the ozonized oxygen and the oxygen dissolved in the water to be discharged is added as oxygen for supply.
The adsorption type gas drier (10) usually comprises two or more adsorption towers (11), (12) in which silica gel or an activated alumina is packed as an adsorbent for removing water. In the case of the two tower arrangement as shown in FIG. 1, when one tower operates for the adsorbing and removing of water, the other tower operates for the regenerating of the adsorbent by feeding hot air from a heater (60) for the gas. After the predetermined time, switching valves (21), (22), (31), (32), (41), (42), (51) and (52) are switched to change the operation for one to the other. Thus, the moisture-removing and the regenerating operations are repeated alternately for the two adsorption towers to dry the discharged oxygen continuously.
However, in the conventional oxygen recycle type ozonizing apparatus, the decrease of ozonizing efficiency is found depending upon the progress of the operating time. In the study of the cause, the presence of a large amount of CO.sub.2 gas and a small amount of volatile organic materials are found in the oxygen returned from the adsorption gas drier. That is, in the conventional apparatus having the reaction towers in the recycle system, the volatile organic materials or CO.sub.2 gas which are contained in the water by the vaporization during the exposing of the treated water to air or which is produced as low molecular organic materials as a result of the reaction of the organic materials dissolved in the water with ozone and volatile organic materials contained in non-treated water are involved in the discharged oxygen. Accordingly, the volatile organic materials can not be satisfactorily removed and the adsorbing and removing of the CO.sub.2 gas contained as a main component of impurity is not substantially attained in the conventional adsorption type gas drier (10) using silica gel or activated alumina as the adsorbent to remove water; thus the ozonizing efficiency decreases.
It is possible to remove a sufficient amount of the CO.sub.2 gas and the volatile organic materials by increasing a volume of the adsorbent. However, this requires a large capacity of the apparatus and the oxygen filled in the adsorption tower should be discharged depending upon the capacity of the apparatus thereby causing a discharge loss. This is inadvantageous from the economical viewpoint.
The inventors have studied and found that when the gas in the oxygen recycle system comprises 90 to 95% of oxygen and 5 to 10% of nitrogen, a superior ozonizing effect can be obtained by using a CO.sub.2 gas concentration of 1 to 2% in comparison with that of zero.